1. Field of the Invention
The present invention generally relates to data converters each of which includes a data leakage prevention function and is applied to a portable terminal unit such as a small size computer, and more particularly to a data converter such as a cryptographic card or an IC card which data converter includes a timer unit so that data is prevented from being read out without a predetermined release operation after the passage of a predetermined time.
2. Description of the Related Art
Information/communication apparatus such as a portable telephone and a computer network have been remarkably widely used of late. It is expected that more portable computers (portable terminal units) will be used in the future to access an in-house information network from outside to download data. In such a situation, it is probable that a user may inadvertently lose a user's portable terminal unit or have the user's portable terminal unit stolen and fall into the hands of someone else. Therefore, it is essential to take measures so that important data stored in a portable terminal unit is prevented from being read by others in such a case as described above.
Thus, conventionally, a variety of encryption software or hardware has been examined and proposed to encrypt data stored in a portable terminal unit so as to provide security for the data.
A cryptographic card, for example, is proposed as encryption hardware to provide security for data stored in a portable terminal unit. According to a technology employing the cryptographic card, a portable terminal unit is enabled only when a predetermined cryptographic card is set therein. Therefore, as long as the predetermined cryptographic card is under the charge of a registered user, data stored in the portable terminal unit is prevented from being read by another person who does not have the predetermined cryptographic card. Further, as a general rule, a cryptographic card of this type additionally includes a function to collate a predetermined password, a signature of the user or a fingerprint of the user input to the cryptographic card with stored data. Thereby, a user authentication is performed to determine whether a cryptographic card holder is the registered user, thus increasing data security.
However, the user's portable terminal unit may be lost or stolen in an enabled state with the cryptographic card set therein. In such a case, the portable terminal unit is properly enabled, so that the important data stored therein may be read by others. That is, sufficient security is not provided for the data.